Composite materials have drastically evolved since their first conception, centered on a simple approach of invoking synergy between different materials. The field has since shifted towards creating so called responsive composites, which exhibit tunable properties triggered via an external stimulus. Such materials have been applied as sensors, actuators and platforms for multi-functional devices.[1-9] Mechanically reconfigurable parts are especially desirable in the field of soft robotics, whereby adaptive components are essential for locomotion.[10-12] Several forms of activation have been applied in responsive composites; common examples include temperature, electromagnetic radiation, electric and magnetic field.[13-19] Mechanical stimulus, although scarce could potentially offer important applications such as self-healing, sound engineering and mechanically adaptive materials. White et al. demonstrated autonomic healing capabilities in a polymeric composite by introducing monomer containing microcapsules, which undergoes polymerization upon contact with the catalyst filled matrix. Crack formation in the composite presumably breaks the microcapsules, which allows the monomer to escape into the matrix and concomitantly polymerizes, thus, preventing further propagation by filling the crack.[20] Synthesis of such microcapsules, however, involve time consuming procedures and a variety of reagents. Furthermore, considering that a catalyst must be incorporated into the matrix, the type of polymer applicable to this method might be limited.
Recently, Tevis et al. developed a simple and low cost method known as SLICE for producing undercooled liquid metal core-shell (undercooled LMCS) particles.[21] This method involves shearing liquid metals as an emulsion to produce spherical-like particles wherein separation of the particles is maintained by concomitantly oxidizing the surface of the metal. cinar et al. applied this technique to produce undercooled liquid metal undercooled particles in a metastable state whereby a normally solid metal maintains itself as a liquid below its melting temperature.[22] Interestingly, it was demonstrated that protective oxide is partly elastic, and further deformation will eventually lead to solidification of the undercooled metal. Utilizing this phase transformation phenomena, these investigators showed that such undercooled liquid metal particles can be used as heat-free solders, triggered by mechanical deformation.